Animal rights groups are trying to increase pressure on Sonoma County to drop a contract with a federal program to control predators that prey on livestock and domestic animals, enlisting an affiliate of the national Humane Society to weigh in on the issue.

Cotati-based Animal Legal Defense Fund has been pushing the Board of Supervisors for months to end the contract, saying the federal program's methods are inhumane and indiscriminate, killing innocent species and failing to consider the ill effects of removing predator species from an ecosystem.

The Humane Society Wildlife Land Trust, which just took over management of an 1,100-acre wildlife preserve near Guerneville, sent a letter to the supervisors in August joining the call for the county to look at less lethal methods. It points to the program used by Marin County, which emphasizes better fencing and livestock protection before turning to methods such as traps, poison or firearms to control nuisance predators.

"It seems that the success of the Marin program is reason enough to look toward careful evaluation and development of a similar comprehensive plan for Sonoma County, adopting as many aspects of it as are workable and adapting it to Sonoma County," wrote trust Executive Director Robert Koons and Vice Chair John Grandy.

The current status of the decades-old contract with the U.S. Department of Agriculture is unclear. After the ALDF protested in June, the supervisors put off what was an otherwise routine vote to renew the contract. Agricultural Commissioner Tony Linegar defended the program but promised to run it by the office of the County Counsel to make sure it did not, as alleged by the ALDF, violate California law protecting wildlife.

That review, however, has dragged on more than two months, with no signal from Linegar as to when it may come back. The contract, worth about $113,000 a year, expired in July, but was temporarily extended while the county reviews the terms.

Linegar did not return a phone call requesting comment last week, but Chris Green, director of legislative affairs for the ALDF, said Linegar had seemed more open in recent meetings to examining the Marin program in more detail.

Green said he hopes to begin meeting individually with supervisors to argue for an end to the federal contract.

The USDA's Wildlife Services, which conducts the predator program, has consistently denied that its methods are cruel or prone to killing large number of animals that are not a threat to livestock or pets.

Spokeswoman Carol Bannerman said the agency does not use steel-jawed or poisoned traps banned in California in a 1998 ballot initiative. She said the agency has worked to find more humane and effective methods of controlling predators in recent decades.

The agency "conducts wildlife damage management activities in compliance with accepted wildlife management guidelines, state laws, and the National Environmental Policy Act," she said.

ALDF and the Humane Society Wildlife Land Trust, however, have been circulating copies of a recent study by researchers from a variety of academic institutions, called "License to Kill," that is critical of the agency.

The agency's methods "risks cascading negative consequences including impoverishment of biodiversity, loss of resilience to biotic invasions, destabilization of populations at lower trophic levels, and loss of many ecosystem services that benefit human society directly and indirectly," the study's authors write. "Lethal predator control is not effective at reducing depredation in the long term."

Bannerman said the study was looking at the program from the perspective of the early 20th century, when killing nuisance predators was common, and ignoring recent efforts to push non-lethal methods, such as encouraging the use of guard dogs to scare predators away from livestock.

Such non-lethal methods deterred or moved more than 18 million animals last year, she said, more than 84 percent of the program's encounters with wildlife.